B3.1 nervous system

• • Stimulus: 

  A detectable change in the internal or external environment of an organism e.g. light, sound or temperature
• • Receptor: 

  A cell or organ which detects a stimulus
• • Neurone: 

  A nerve cell, specially adapted to carry electrical charges, called nerve impulses from one part of the body to another
• • Sensory neurone: 

  A neurone which carries nerve impulses from receptors to the central nervous system
• • Motor neurone: 

  A neurone which carries nerve impulses from the central nervous system to effectors
• • Relay neurone: 

  A neurone that acts as a coordinator, transmitting impulses from the sensory to the motor neurone in the spinal cord
• • Effector: 

  A cell, tissue, organ or organ system that responds to a stimulus
• • Voluntary response: 

  A nerve pathway which produces a conscious response to a stimulus
• • Reflex response:

   A nerve pathway which produces an automatic response to a stimulus
• • Synapse: A gap between two neurones
• • Axon: 

  A single long fibre within a neurone which carries a nervous impulse away from the cell body
• • Electrical impulse: 

  A signal which is passed through the nervous system as electrical charge to instigate a response
• • Central nervous system (CNS) 


  – The part of the nervous system which includes brain and spinal cord
• • Peripheral nervous system (PNS) 
  • – All of the nerves in the body which extend from the CNS
• • The neurones that are found in the CNS are relay neurones
• • The central nervous system (CNS) consists of the brain and spinal cord
  • It is responsible for coordinating the response by directing the electrical impulse to the correct effector
• • Peripheral nervous system (PNS) is made up of all of the nerves in the body that extend from the CNS
  • It also includes sensory receptors which detect stimuli from the surroundings
• A neurone is a nerve cell

  A) dendrites

  B) axon

  C) myelin sheath

  
• • Electrical impulses cannot cross synapses, instead chemicals called neurotransmitters (such as dopamine and serotonin) transmit the impulse from one neurone to the next
  • This is the only part of the nervous system where messages are chemical as opposed to electrical
  • Neurotransmitters diffuse across the synapse which slows down the transmission of electrical impulses
  • Synapses ensure that impulses only travel in one direction
• An involuntary (or reflex) response does not involve the brain as the coordinator of the reaction and you are not aware you have completed it until after you have carried it out

  • The passage of information in an involuntary response is called a reflex arc
  • Involuntary actions are usually ones which are rapid and are essential to basic survival
• • A voluntary response is one where you make a conscious decision to carry out a particular action therefore it starts with your brain
  • Voluntary responses often take longer than involuntary responses as we consider what the response might be before doing it
• • Sensory neurones carry impulses from sense organs to the CNS (brain or spinal cord)
• • Relay neurones are found inside the CNS and connect sensory and motor neurones
• • Motor neurones carry impulses from the CNS to effectors (muscles or glands)
• There are three different types of neurones in the reflex arc

  A) sensory

  B) relay

  C) motor

  D) myelin sheath

  E) axon

  F) dendrite

  G) axon

  
• • The eye contains two types of receptor cell: rod cells which are sensitive to light intensity and cone cells which are sensitive to different wavelengths of visible light (colour)
• where are rod and cone cells located?


  retina
• structure of an eye.

  A) cornea

  B) iris

  C) pupil

  D) lens

  E) ciliary muscle

  F) retina

  G) optic nerve

  
• what does the cornea do?

  transparent coating that refracts light as it enters eye.
• what does the iris do?

  control how much light enters the eye
• what does the lens do?

  transparent disc that changes shape to focus light onto retina
• what does the retina do?

  contains light receptor cells
• what does the pupil do?

  hole that allows light into the eye#
• what happens in dim light?

  the pupil dilates (widens) in order to allow as much light into the eye as possible
• what happens in bright light?

  the pupil constricts (narrows) in order to prevent too much light entering the eye and damaging the retina
• • To focus on a close up object:
  • Ciliary muscles contract
  • Suspensory ligaments slacken
  • This allows lens to become fatter
  • Light is refracted more
• • To focus on a distant object:
  • Ciliary muscles relax
  • Suspensory ligaments are pulled tight
  • The lens is pulled thinner
  • Light is refracted less
• • People who suffer from colour blindness cannot distinguish between certain colours and in rare cases, cannot see colours at all. why?
  • This happens because the cones in the retina do not work properly or are absent
• structure of brain.

  A) hypothalamus

  B) homeostasis

  C) cerebrum

  D) voluntary

  E) memory

  F) cerebellum

  G) coordination

  H) pituitary gland

  I) other glands

  J) medulla

  K) involuntary

  L) heart

  M) breathing

  
• • The cerebral cortex: 

  This is the outer layer of the brain which is divided into two hemispheres. It’s highly folded and is responsible for higher-order processes such as intelligence, memory, consciousness and personality